Field of the Invention
The present invention relates to an optical apparatus, e.g., an adapter which includes a light amount adjustment unit configured to change transmissivity of imaging light through change in physical property thereof, an interchangeable lens, or a camera main body, and to a camera system using the same.
Description of the Related Art
For the purpose of connecting interchangeable lenses having different mount shapes to a camera main body, an adapter has been hitherto used. Reasons for the different mount shapes include difference in image size and difference in flange focal distance.
In recent years, compact and lightweight mirrorless single-lens cameras in which a mirror unit of a single-lens reflex camera is removed are becoming widespread. Compared with a single-lens reflex camera, a mirrorless single-lens camera is designed to have a shorter flange focal distance, and has a different mount shape.
Due to the removal of the mirror unit, the mirrorless single-lens camera described above is optimized for a contrast AF system, and is thus suitable for taking moving images, while a single-lens reflex camera uses both the contrast AF system and a phase-difference AF system. With such background circumstances, as mirrorless single-lens cameras become widespread, there is an increasing demand for taking moving images with a digital camera.
Meanwhile, a stop configured to change an area of a hole through which light passes in order to adjust the amount of incident imaging light is indispensable for an interchangeable lens. As the stop, there is often used a mechanical stop (that mechanically changes the area through which the imaging light passes) with a stepping motor or the like serving as a drive source thereof. A mechanical stop structurally produces driving noise. Therefore, when a moving image is taken together with sound recording, a problem that the driving noise is also recorded arises. Further, the driving noise caused by the mechanical stop is produced not only when a moving image is taken but also when a still image is taken. Under the circumstances where quietness is required, e.g., in a concert hall, the driving noise is not preferred.
In Japanese Patent Application Laid-Open No. 2012-203142, there is disclosed an attachment lens device including, in an attachment mounted between an imaging lens and a camera main body, a stop unit that can change an aperture diameter to limit the amount of incident light from the imaging lens.
In Japanese Patent Application Laid-Open No. 2012-203142, the attachment lens device includes the stop that can change the aperture diameter. The stop is mounted between a master lens and the camera main body, and thus is arranged at a position different from the position of a focal point in the imaging lens. In this case, the arrangement of the stop at a position different from the position of the focal point in the imaging lens causes vignetting in which a periphery of an image pickup surface becomes darker.
Further, when a mechanical stop is used as a stop in an attachment lens, there arises a problem in that driving noise is caused when a moving image or a still image is taken.